The initial rapid filling is mainly augmented by ventricular suction which results from ventricular untwisting and the return of each ventricular muscle fiber to its slack length. Ventricular filling (e-a): As the AV valves open at point (e), ventricular filling starts.This phase usually lasts for 8% of the cardiac cycle. The ventricles generate negative pressure without changing their volume (isovolumetric) so that the ventricular pressure becomes lower than the atrial pressure. Isovolumetric relaxation (d-e): When the ventricular pressures drop below the diastolic aortic and pulmonary pressures (80 mmHg and 10 mmHg respectively), the aortic and pulmonary valves close producing the second heart sound (point d).This phase usually lasts for 15% of the cardiac cycle. However, some forward flow of blood continues secondary to remnant kinetic energy from the previous phase. Repolarization leads to a rapid decline in ventricular pressures and hence the reduced rate of ejection. Reduced ejection (c-d): This phase marks the beginning of ventricular repolarization as depicted by the onset of the T wave on the EKG.This phase usually lasts for 13% of the cardiac cycle. The arterial pressure increases until reaching its maximum at point (c). Rapid ejection (b-c): As the semilunar valves open at point (b), there is a rapid ejection of blood due to increased ventricular contractility.This phase usually lasts for 6% of the cardiac cycle. With all valves closed, the ventricle generates positive pressure without any change in its volume (isovolumetric) to overcome the semilunar valves resistance that open at point (b).
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